Field plate anchoring structure for trench-based semiconductor devices

A semiconductor device, comprising:

• a semiconductor substrate;
• a gate trench extending from a first main surface of the semiconductor substrate into the semiconductor substrate;
• a field plate trench extending from the first main surface into the semiconductor substrate and laterally spaced apart from the gate trench, the field plate trench having one or more sidewalls and a bottom;
• a field plate in the field plate trench;
• an air gap separating the field plate from the one or more sidewalls and the bottom of the field plate trench;
• a space in a central part of the field plate;
• and
• an electrically insulative material occupying the space in the central part of the field plate and anchoring the field plate to the semiconductor substrate by spanning the air gap at the bottom of the field plate trench.

A method of producing a semiconductor device, the method comprising:

• etching a first gate trench and a second gate trench into a first main surface of a semiconductor substrate, the first and second gate trenches delimiting a semiconductor mesa;
• etching a field plate trench into the first main surface, the field plate trench extending through the semiconductor mesa;
• forming a field plate in the field plate trench, the field plate being separated from each sidewall and a bottom of the field plate trench by an air gap, the field plate having a space in a central part of the field plate;
• and
• anchoring the field plate to the semiconductor substrate at the bottom of the field plate trench by an electrically insulative material that occupies the space in the central part of the field plate, the electrically insulative material spanning the air gap to contact the semiconductor substrate at the bottom of the field plate trench.